The present invention relates to a water treatment method for electrochemically treating water to be treated containing oil droplets and microorganisms.
Recently, industrial water is reused extensively, wherein various impurities contained in industrial water which has been used once are removed through separation so that the industrial water can be reused. In general, impurities contained in each industrial water are already-known in terms of components, and therefore, the components are separated and removed after being aimed in many cases.
For example, processing water used for food processing is abundant in nutritive substances, and therefore microorganisms such as bacteria therein breed, which makes it impossible to reuse the processing water without treating as processing water for food processing. It is impossible to act on these microorganisms such as bacteria with anti-mold agents or with sterilizers, because it is apprehended that the anti-mold agents or sterilizers used are mixed in foods. Therefore, it has been desired that such processing water is simply treated and reused as water in an aseptic condition.
As a water treatment method free from the disadvantages mentioned above, TOKKAIHEI Nos. 3-224686 and 4-27488 disclose a method to treat electrochemically. In this method, it is possible to treat a huge amount of water efficiently without using any specific chemicals.
However, in the case of processing water used for food processing, once it is used, oil ingredients liquated out of the foods become oil droplets and are mixed in the processing water. When water to be treated containing oil droplets is treated, without taking any action on it, in the method mentioned above, blocking on an electrode is caused, or the surface of the electrode is masked with oil ingredients, which makes sterilizing treatment impossible in a short period of time. In addition, the oil droplets serve as the nutrition source for microorganisms and bacteria existing in processing water, or the oil droplets stick to processed foods to adversely affect the foods including lowering commercial value of the foods. In particular, it is desired that washing water for broilers or bean curd is used repeatedly many times because of low cooling temperature, from the viewpoint of energy conservation. However, as stated above, processing water used for the aforesaid items is mixed with oil droplets after it is once used, and it adversely affects in many ways, thus an appropriate method for eliminating the oil droplets has been desired.
Heretofore, these oil droplets have been scrubbed out through methods including one for removing them physically using microfilters and others, and one for removing them after adding activated carbons or coagulants to them. However, expenses for the removal of the oil droplets in those methods have been higher than expected and treatment capacity in each of the methods has been low, thus, the methods have been regarded to be problematic.
On the other hand, for separation of suspended substances in water, there are available floatation separation methods wherein there are introduced fine air bubbles each sticking to a suspended particle to separate it. One of the floatation separation methods is an electrolytic floatation separation method.
With regard to separation of oil droplets through an electrolytic floatation separation method, TOKKAIHEI 2-40286, for example, discloses that fine particles contained in grinding oil used in machining by machine tools or a colloid solution used in the field of civil engineering and construction are electrolyzed, and metal ions generated by the electrolysis are caused to stick to fine particles and ions hydroxide and to surface to be removed. TOKKAIHEI 5-337472 discloses that when removing suspended substances remaining in waste water treated with coagulants, the water to be treated passes through a plurality of electrodes arranged horizontally and further passes through electrodes arranged vertically to be electrolyzed in the course of the passage, thus suspended substances become flock and are caused to surface to be removed. In TOKKAIHEI 2-222771, a plurality of electrodes are provided obliquely so that voltage can be impressed uniformly on water to be treated to accelerate generation of flock bubbles. In TOKKAIHEI 4-300694, there are provided a cylindrical aluminum anode and a thin aluminum pipe representing a cathode located at the center of the anode, and water to be treated is caused to pass through the cylinder to be electrolyzed so that suspended substances may surface to be removed. Since scale is generated and sticks to an aluminum electrode, especially cathode, in an electrolytic floatation method, a method to prevent that is disclosed in TOKKAIHEI 6-142407. TOKKAIHEI 5-50070 discloses that when a plurality of insoluble electrodes each being a metal base of titanium, tantalum, or niobium covered with platinum having a thickness of several microns are used as an electrode, and a polarity of the electrode is reversed at certain intervals, it is possible to clean water to be treated for a long time through electrolytic floatation without replacing electrodes. Furthermore, TOKKAIHEI 5-253509 discloses that a plurality of aluminum sheets are used as an electrode, and polarity of the electrodes is reversed at certain intervals to separate oil components from oil-containing bilge water generated from an engine room of a ship through an electrolytic floatation method. However, when water from which oil drops have been separated through the electrolytic floatation method is treated by the method employing a fix bed type electrolytic tank described in TOKKAIHEIs 3-224686 and 4-27488, metal ions generated in the electrolytic floatation method are mixed in the water to be treated, and compounds of the metal ions cause clogging on electrodes in the fixed bed type electrolytic tank, making sterilization impossible in a short period of time, which has been a serious problem.